In the manufacture of tubing, a continuous tube is emitted from a tube mill at a high speed and the tube is cut into desired lengths as needed for specified usage or for convenient storage or shipping. The conventional cutting method uses a guillotine type cutter which chops the tube in a downward motion and is then retracted by an upward motion. In order not to interfere with the continuous advance of the tube, the knife, carried on a shuttle, moves in the direction of tube advance during cutting and retracting. Then the shuttle must return the knife to a start position for the next cut. Thus the alternating motion in two directions, forward and back motion of the shuttle and knife as well as up and down motion of the knife, is inefficient from the standpoint of overcoming inertia when reversing the movements. The inertia is substantial due to the considerable mass of the cutting mechanism. In addition, the time required for such cutting procedure places a limit on the production rate of the tubing.
It has been proposed to use a rotary knife motion for such purposes wherein a knife is moved in an arc during the cut and is then stopped and restarted in time for the next cut. In this case, the inertia of the knife must be overcome twice for each cut.